No system will ever be perfect. I think that is one of the fundamental problems in this country, and with human thinking in general.
Don't let the perfect be the enemy of the good.
No system we ever devise will be 100% perfect, with 0 false negatives or false positives. We will sometimes never find the murderer and we will sometimes punish the innocent. But what we can control is how we handle the 99% of cases in which we got it right.
The way around it is to have expedition processes for cases which are clear cut.
This case for example at the Batman shooting doesn't even need to go to trial. He killed all those people, there's tens of witnesses, and so forth. All his human rights should be forfeited.
The issue is determining where the line be drawn in such cases. Also, lots of victims/their families like to see a trial and to have their say, for closure.